Vaporizers for medical respirators

ABSTRACT

A vaporizer for use in a medical respirator for supplying a mixture of patient gas and vapor to a patient during an inspiratory period of the respirator. The vaporizer has a source of patient gas connected thereto and a pair of sealed vessels, each having a connection to the source of gas. When the gas is fed to the vessel containing the liquid, the gas therein becomes saturated. A changeover switch is provided in the connection to the vessels so that alternately the supply of gas is fed to the vessels and to a patient via a patient supply connection. Each vessel is provided with means for adjusting the volume therein so as to control the percentage of saturation of the gas which is passed to the patient from the vessels and so as to control the total volume of gas passed to the patient during each inspiratory period.

United States -Patent [2i] Appl.No.: 6,195

[30] Foreign Application Priority Data Bushman 1 May 2', 1972 1VAPORIZERS FOR MEDICAL oams N PATEiflISOR APPLICATIONS RESPIRATORS778,787 7/1957 Great Britain ..128/188 [72] Inventor: Mm Bum, Cambridge,Em 1,183,738 3/1970 Great Britain; ....12s/1ss gland 1,256,023 2/1961France ..128/182 [73] Assign: P" Limited Cambridge England PrimaryExaminer-Richard A. Gaudet [22] Filed: Jan. 27, 1970 AssistantExaminer-G. F. Dunne Attorney-Frank R. Trifari [57] ABSTRACT A vaporizerfor use in a medical res irator for su i in a mix- P PP Y 8 ture ofpatient gas and vapor to a patient during an inspiratory Feb. 5, 1969Great Britain ..6,17 1/69 p i f the respirator The vaporizer has aSource of patient gas connected thereto and a pair of sealed vessels,each having ..l28/188A,61128/:s4/5d8) a connccfion to the source of 8%when the gas is fed to the 58] i 3 197 vessel containing the liquid, thegas therein becomes satu- 128 I209 6 8 145 26i/62 rated. A changeoverswitch is provided in the connection to V V w the vessels so thatalternately the supply of gas is fed to the vessels and to a patient viaa patient supply connection. Each [56] References Cited vessel isprovided with means for adjusting the volume therein so as to controlthe percentage of saturation of the gas which is UNITED STATES PATENTSpassed to the patient from the vessels and so as to control the 3,527 ,2i 3 9/ l 970 Schreiber i 28/ i 88 total volume of gas passed to thepatient during each inspirato- 3,126,001 3/1964 Engstrdm ..128/l88 X ryperiod.

Patented May 2, 1972 3,659,601

2 Sheets-Sheet 1 INVENTOR.

JOHN ANDREW BUSH MAN AGENT Patented May 2 1972 2 Sheets-Sheet 2 B2 j cozINVENTOR.

JOHN ANDREW BUSH M AN AGENT VAPORIZERS FOR MEDICAL RESPIRATORS Theinvention relates to vaporizing means for medical respirators whereby avariable controlledamount of vapor is included in the respiratory gasflow to a patient.

A known type of vaporizer allows patient gas to pass from a source tothe patient along one path provided with a first restrictive means orthrottle valve and along another path comprising a second restrictivemeans or throttle valve and a vaporizing chamber containing liquid. Thevaporizing chamber is frequently provided with baffles and :wickspartially exposed to the gas to assist in the entrainment of vapor fromthe liquid. The two restrictive means are operated by a common controlknob to determine the relative amounts of gas passing through the twopaths and, hence, the percentage saturation of the total amount of gaspassingto the patient.

Such Vaporizers are normally used in minute/divider" type respirators,i.e. respirators employing a master flow control supplying a constantflow of gas at substantially atmospheric pressure. Calibration curvesfrom such vaporizers show that the percentage saturation is not constantfor all flow rates, and they are therefore not suitable for use withintermittent flow. Additionally, such Vaporizers require that adjustmentof the combined throttle valves does not affect the total flow fromsource to patient throughout this range of control of saturationpercentage. Where this range is relatively large, difficulties arefrequently encountered at least at one end of the control range whichresult in a non-linear scale for the saturation control and/or requirethe throttle valves and the path to the container to have a specialconstruction (e.g. U.K. Patents 966,797 and 1,001,854).

The present invention provides a vaporizer suitable for intermittentflow which avoids the use of linked throttle valves.

From one aspect, the present invention provides a vaporizer comprising asealed vessel containing a liquid partially filling the vessel, and apath to and/or from the vessel which is periodically alternatelyconnected by changeover switching means to a source of patient gas at afirst pressure higher than atmospheric pressure and to a patient, thegas within the vessel being saturated with vapor from the liquid and thepercentage saturation of the gas when passed to the patient at a secondpressure which is substantially atmospheric pressure being determined bythe difference between the first and second pressures.

Preferably the vessel is of adjustable volume in order that both thequantity of gas stored therein during connection to the source and thepercentage saturation of gas delivered to a patient may be controlled.

From a second aspect, the invention provides a vaporizer comprising afirst sealed vessel containing a liquid, a second sealed vessel, andchangeover switching means alternately connecting both vessels in unisonto a source of patient gas at higher than atmospheric pressure and to apatient, the gas within the first vessel being saturated with vapor fromthe said liquid, the percentage saturation of the gas passed to thepatient from both vessels being determined by the relative quantities ofthe gas-and-vapor and gas contained by the first and second vesselsrespectively, the said quantities also determining the total volume ofgas passed to the patient during each inspiratory period. Preferably,the volume of each of the two vessels is adjustable.

The various features of the present invention will be apparent from thefollowing description of exemplary embodiments thereof taken inconjunction with the accompanying drawings, in which:

FIG. 1 shows a vaporizer for a respirator giving a fixed Tidal Volume.

FIG. 2 shows the vaporizer of FIG. 1 modified to enable Tidal Volume tobe varied.

In FIG. 1, a fixed pressure source of patient gas is applied to port N2,gas therefrom passing via a line 1 to a port A] of a changeover valveC01 .which in a first expiratory position, in-

' dicated by a solid line, allows passage of the gas to port C1 of thevalve. From port C1 the gas passes via a line 7A to a first volume,partially filled with liquid to a level as indicated by a broken line 3,the volume available for gas and liquid vapor being determined by theposition of a piston 9A in a cylinder 8A and by the liquid'level. Duringthe expiratory period with valve CO1 establishing a gas passage as shownby a solid line, gas within the volume is saturated, i.e. will take upno more vapor from the liquid. Increase of the-pressure of the sourcewill increase the amount of gas relative to vapor in the volume at agiven temperature, i.e. will decrease the percentage saturation onrelease of the volume of gas to atmospheric pressure. A decrease inthesource pressure is accompanied by an increase in percentage saturationof the gas. Variation of source pressure also alters the quantity ofgas/vapor stored in the first volume, but at a fixed, greater thanatmospheric, pressure, gas

and vapor have a fixed ratio irrespective of the size of the volume,variation of which by movement of piston 9A merely altering the quantityof gas/vapor stored.

Gas from port N2 also. passes via a line 6A to a port A2 of a secondchangeover valve CO2 which in its first position permits gas to flow asshown by a solid line to a port C2. From this latter port the gas isthen passed via a line 73 to a second volume formed within a cylinder 88by a piston 98. The quantity of gas stored in the second volume issimilarly a product of the gas pressure and size of volume as determinedby the position of piston 98.

Piston rods 10A and 108 control the position of the respective pistons9A and 9B and mechanical linkage of the rods, indicated by a brokenline, is arranged to move the pistons in opposite directions so that thesum of volumes in cylinder 8A and 8B, and hence of the gas/vapor and gastherein, is constant.

In asecond inspiratory position of valves CO1 and CO2 gas passages areestablished, as indicated by broken lines, between respectiveports C1,B1 and C2, B2. Ports B1 and B2 are both connected to a common path line4 leading to a patient and thegas/vapor and gas will therefore flow fromthe two volumes to the patient, the total amount of gas relative tovapor being determined by the relative positions of the two pistons. Theoperating means of the mechanical linkage may thus be calibrated interms of percentage saturation.

In the vaporizer described above, the source pressure and the sum of thevolumes are both constant and the Tidal Volume of gas delivered to apatient will also be constant. Decrease of such Tidal Volume may beachieved by curtailing the time during which discharge from the volumeoccurs, e.g. by providing at least one'restriction and switch betweenports B1, B2 and the patient and closing'the path to the patient beforepressure in the volumes has fallen to the minimum. As variable volumesare involved in determining saturation percentage, compensation foralterations in the discharge time constant (Volume X Flow Resistance)have then to be provided.

Preferably such variation of Tidal Volume is also obtained by variationof the two volumesv of FIG. 1 as shown in FIG. 2, which also shows meanswhereby a plurality of patient gases may be mixed in desiredproportions.

In FIG. 2, two different patient gas sources are connected to ports N3and N4 having regulators PR3 and PR4 and flow controls FC3, FC4respectively in the paths to a common pipe line 11. Preferably theregulators are coupled together and ar' ranged so that they both have agiven pressure output or one or the other alone has the given outputwhich may be, for example 60 PSI. With pressure output from bothregulators, each flow control determines the amount of gas passingtherethrough in unit time and the setting of these controls thereforedetermines the mixture of gases in line 11 linking their outputs. Pipeline 11 is connected to lines 1 and 6A feeding ports A1 and A2 ofchangeover valves CO1 and CO2, whose ports B1 and B2 pass gas saturatedto a required degree through lines 4 and 68 towards a patient. Twocylinders 8C and are connected to the ports Cl and C2 of valves CO1 andCO2 by lines 7A and 78 respectively. Cylinder 8C has two opposed pistons9C and 9CC having piston rods 10C and CC respectively. Similarlycylinder 8D has pistons 9D and 9DD and rods 10D and 10DD. Cylinder 8Ccontains a quantity of liquid, for mixing with the gas, whose level isindicated by a broken line 3. A bar 12 is rigidly attached to pistonrods 10C and 10D and carries a nut 13 engaged with a threaded rod 14,carried by bearings, not shown, so that it may be rotated by an attachedknob 15 to move pistons 9C and 9D and hence adjust the Tidal Volume.Piston rod 10DD is coupled to a bar 16 by means of a pin 17 in slidableengagement with a slot 18 in bar 16, rod l0CC being similarly coupled bya pin 19 co-operating with another slot 20 in bar 16. Bar 16 is arrangedto pivot on a pin 21, slidably engaged in a further slot 22 in bar 16,carried by a member 23 so that as piston 9CC moves in one direction,piston 9DD moves in an opposite direction. An extension of bar 16carries a pivotally mounted nut 24 which is engaged with a threaded rod25, rotatable in bearings, not shown, to which is attached a knob 26.Rotation of knob 26 will thus cause variation of percentage saturationand its angular rotation may thus be calibrated in such terms.

Depending on the relative amounts of piston movement, the maximum volumeavailable for gas within the cylinders and the desired accuracy of theabove scale, a correcting device may be required to compensate for thechange in effective volume ratios at high and low percentage saturationsettings as Tidal Volume is altered.

This is accomplished in the embodiment described by movement of thepivot 21. Member 23 is arranged to slide in guides, not shown, and hasattached arms 27 carrying roller cam followers 28. These are inengagement with the faces of a cam nut 29, which is engaged with rod 14.Nut 29 is guided and prevented from turning by means not shown and willtraverse rod 14 during rotation of knob 15 and rod 14 to alter therelative distances between pins 21 and 17, and pins 21 and 19. Nut 29and pistons 9D and 9C move together, the cam profile being such that thenecessary change in pivot position is made to retain calibration of thepercentage saturation control. r

Although when pivot 21 is not in its midposition, alteration of thepercentage saturation control will affect the calibration of the TidalVolume control, the effect is not large as movement of piston 9DD isstill largely compensated by opposite movement of piston 9CC. The effectmay be further reduced by arranging that the range of control ofpercentage saturation available is greater than normally required sothat extreme settings are not normally used.

In both FIGS. 1 and 2 gas in the two volumes is, at-the com-- mencementof an inspiratory period, at the same pressure as the source, e.g. 60PSI, and a very rapid flow to the patients lungs would occur for a shortperiod of time. A flow control,

similar to that preceding the known type of vaporizer, between thepatient and line 4 is therefore necessary to avoid too rapid inflationof the lungs.

What is claimed is:

1. A vaporizer apparatus for use in a medical respirator, comprising afirst sealed vessel containing a liquid, a second sealed vessel, asource of patient gas, a means of supply of gas to a patient, changeoverswitching means alternately connecting both vessels in unison to saidsource of patient gas at higher than atmospheric pressure and to saidpatient supply means, the gas within the first vessel being saturatedwith vapor from the said liquid, the percentage saturation of the gaspassed to the patient from both vessels being determined by the relativequantities of the gas-andvapor and gas contained by the first and secondvessels respectively, the said quantities also determining the totalvolume of gas passed to the patient during each inspiratory period, andmeans for adjusting the volume of each of the said vessels including afirst adjusting means for varying the volumes of the two vessels inopposite senses to control the percentage saturation of gas passed tothe patient, and further including a second adjusting means for varyingthe volumes in the same sense to control the total quantity of gas andvapor passed to the patient via said means of supply to the patient inan inspiratory period.

2. The vaporizer apparatus according to claim 1 further comprising meansmechanically interrelating the first and second adjusting means, wherebythe adjustment of either one of said first and second adjusting meansefi'ecting the two volumes such that the percentage saturation of gaspassed to the patient remains substantially constant when the volume ofgas passed to a patient during each inspiratory period is changed.

3. The vaporizer apparatus according to claim 1 wherein said adjustingmeans for varying the volume of the two vessels comprises a firstmovable wall within each vessel movement of which varies the volume ofthe vessel concerned, said first movable walls being mechanicallycoupled by a first mechanical coupling means adjustment of which by thefirst adjusting means causes the volumes of the two vessels to change inopposite senses to control the percentage saturation of gas passed tothe patient.

4. The vaporizer apparatus according to claim 3 further comprising asecond movable wall within each of said vessels, movement of whichvaries the volume of the vessel concerned, said second movable wallsbeing mechanically coupled by a second mechanical coupling meansadjustment of which by a second adjusting means causes the volumes ofthe two vessels to change in the same sense to control the quantity ofgas and vapor passed to a patient via said patient gas supply means inan inspiratory period.

5. The vaporizer apparatus according to claim 4 further comprising athird mechanical coupling means interconnecting said first and secondcoupling and adjustment means, said third mechanical coupling meansbeing arranged to alter the ratio of opposed incremental volume changesmade by the first means on operation of the second means, whereby anychange in the percentage saturation of gas passed to a patient wouldotherwise result from a change in ,the sum of the volumes by operationof the second adjustable means is automatically compensated by saidthird mechanical coupling means.

6. The vaporizer'according to claim 4 wherein each vessel is formed by acylinder, and wherein said movable walls are formed by movably mountedpistons.

7. A vaporizer apparatus for use in a medical respirator comprising afirst sealed vessel containing a liquid partially filling the vessel, asecond sealed vessel, a movable wall within each of said vessels forcontrolling the volume therein, a source of patient gas for providing asupply of patient gas at a first pressure which is higher thanatmospheric pressure, connection means for communicating said source ofpatient gas to both of said vessels simultaneously, means for supplyinggas from said vessels to a patient, changeover switching means foralternately connecting said vessels to said supply of patient gas andthe patient so that when the vessels communicate with the supply of gasthe gas within said first vessel will become saturated with vapor fromthe liquid contained therein, means connected to said movable walls forcausing adjustment thereof to vary the volume within the vessels so thatthe degree of saturation of the gas passed to the patient when saidvessels are caused to communicate therewith is thereby controlled by therelative amount of vapor saturated gas contained in said first vesseland gas in said second vessel, said amounts being determined by thetotal volume of gas passed to the patient during each inspiratoryperiod.

8. The vaporizer apparatus according to claim 7 wherein said meansconnected to said movable walls for causing adjustment thereof iscontrolled so that an incremental change in the volume of said firstvessel in one sense will be accompanied by an incremental change of thesame magnitude in the opposite sense in the volume of said second vesselso that the combined volume of both of said vessels will remainconstant.

9. The vaporizer apparatus according to claim 7 further comprising meansconnected to both said movable walls of said vessels for causingsimultaneous adjustment thereof in equal amounts and in the same senseso as to vary the combined volume of said vessels.

ll l t t

1. A vaporizer apparatus for use in a medical respirator, comprising afirst sealed vessel containing a liquid, a second sealed vessel, asource of patient gas, a means of supply of gas to a patient, changeoverswitching means alternately connecting both vessels in unison to saidsource of patient gas at higher than atmospheric pressure and to saidpatient supply means, the gas within the first vessel being saturatedwith vapor from the said liquid, the percentage saturation of the gaspassed to the patient from both vessels being determined by the relativequantities of the gas-and-vapor and gas contained by the first andsecond vessels respectively, the said quantities also determining thetotal volume of gas passed to the patient during each inspiratoryperiod, and means for adjusting the volume of each of the said vesselsincluding a first adjusting means for varying the volumes of the twovessels in opposite senses to control the percentage saturation of gaspassed to the patient, and further including a second adjusting meansfor varying the volumes in the same sense to control the total quantityof gas and vapor passed to the patient via said means of supply to thepatient in an inspiratory period.
 2. The vaporizer apparatus accordingto claim 1 further comprising means mechanically interrelating the firstand second adjusting means, whereby the adjustment of either one of saidfirst and second adjusting means effecting the two volumes such that thepercentage saturation of gas passed to the patient remains substantiallyconstant when the volume of gas passed to a patient during eachinspiratory period is changed.
 3. The vaporizer apparatus according toclaim 1 wherein said adjusting means for varying the volume of the twovessels comprises a first movable wall within each vessel movement ofwhich varies the volume of the vessel concerned, said first movablewalls being mechanically coupled by a first mechanical coupling meansadjustment of which by the first adjusting means causes the volumes ofthe two vessels to change in opposite senses to control the percentagesaturation of gas passed to the patient.
 4. The vaporizer apparatusaccording to claim 3 further comprising a second movable wall withineach of said vessels, movement of which varies the volume of the vesselconcerned, said second movable walls being mechanically coupled by asecond mechanical coupling means adjustment of which by a secondadjusting means causes the volumes of the two vessels to change in thesame sense to control the quantity of gas and vapor passed to a patientvia said patient gas supply means in an inspiratory period.
 5. Thevaporizer apparatus according to claim 4 further comprising a thirdmechanical coupling means interconnecting said first and second couplingand adjustment means, said third mechanical coupling means beingarranged to alter the ratio of opposed incremental volume changes madeby the first mEans on operation of the second means, whereby any changein the percentage saturation of gas passed to a patient would otherwiseresult from a change in the sum of the volumes by operation of thesecond adjustable means is automatically compensated by said thirdmechanical coupling means.
 6. The vaporizer according to claim 4 whereineach vessel is formed by a cylinder, and wherein said movable walls areformed by movably mounted pistons.
 7. A vaporizer apparatus for use in amedical respirator comprising a first sealed vessel containing a liquidpartially filling the vessel, a second sealed vessel, a movable wallwithin each of said vessels for controlling the volume therein, a sourceof patient gas for providing a supply of patient gas at a first pressurewhich is higher than atmospheric pressure, connection means forcommunicating said source of patient gas to both of said vesselssimultaneously, means for supplying gas from said vessels to a patient,changeover switching means for alternately connecting said vessels tosaid supply of patient gas and the patient so that when the vesselscommunicate with the supply of gas the gas within said first vessel willbecome saturated with vapor from the liquid contained therein, meansconnected to said movable walls for causing adjustment thereof to varythe volume within the vessels so that the degree of saturation of thegas passed to the patient when said vessels are caused to communicatetherewith is thereby controlled by the relative amount of vaporsaturated gas contained in said first vessel and gas in said secondvessel, said amounts being determined by the total volume of gas passedto the patient during each inspiratory period.
 8. The vaporizerapparatus according to claim 7 wherein said means connected to saidmovable walls for causing adjustment thereof is controlled so that anincremental change in the volume of said first vessel in one sense willbe accompanied by an incremental change of the same magnitude in theopposite sense in the volume of said second vessel so that the combinedvolume of both of said vessels will remain constant.
 9. The vaporizerapparatus according to claim 7 further comprising means connected toboth said movable walls of said vessels for causing simultaneousadjustment thereof in equal amounts and in the same sense so as to varythe combined volume of said vessels.